Tom, Lucy, Osama,
On 13/08/16 14:25, Bob Briscoe wrote:
*2.2/ GUE versions*
S3.1
The hack in GUE v1 to compress out the GUE header for direct
encapsulation of IP (v4 or v6) seems neat, but it is also /extremely
dangerous/. If GUE becomes successful, it would prevent incremental
deployment of any new version of IP starting 0b10, 0b11 or 0b00. Because:
* S.5.4 says drop an unknown version field, so IP cannot be upgraded
independently from GUE code.
* A version of IP starting 0b00 would be mistaken for GUE.
The latter might sound unlikely, but bear in mind that:
* you don't know what ideas might come up in future for using multiple
versions of IP - the IP version field could become important.
* a future version of IP might wrap the version field, because 0x0-0x3
are no longer used (a version only has to be a unique tag, it doesn't
have to increase).
Pls ignore the above.
Brain fart: I was thinking any version of IP would have to directly
follow the UDP header, but (of course) the encapsulator could include a
GUE v0 header in front of any future IP header that did not start with 0b01.
Bob
[Aside: If you prefer an equally dangerous hack (perhaps because you
don't believe there will ever be a version of IP beyond v6), you could
have reduced the Ver field to the first single bit by making GUEv0 the
one without a GUE header, and GUEv1 the one with. This would have
given more space for the Hlen field (see my concern in A2.1/ "HLEN too
small" above and my idea in a separate email to remove the C flag).]
In the separate email about redesign, I'll describe an alternative
approach that always fits the base GUE protocol into 4B, or even
within the 8B UDP header (see C6/ Wire Protocol; it comes from an idea
to develop GUT into what I called Gutless
<https://www.ietf.org/mail-archive/web/tsvwg/current/msg09854.html>,
back in Feb 2010).
--
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Bob Briscoe http://bobbriscoe.net/
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